Stress analysis of ultra-thin silicon chip-on-foil electronic assembly under bending

Abstract

In this paper we investigate the bending-induced uniaxial stress at the top of ultra-thin (thickness ⩽20 μm) single-crystal silicon (Si) chips adhesively attached with the aid of an epoxy glue to soft polymeric substrate through combined theoretical and experimental methods. Stress is first determined analytically and numerically using dedicated models. The theoretical results are validated experimentally through piezoresistive measurements performed on complementary metal-oxide-semiconductor (CMOS) transistors built on specially designed chips, and through micro-Raman spectroscopy investigation. Stress analysis of strained ultra-thin chips with CMOS circuitry is crucial, not only for the accurate evaluation of the piezoresistive behavior of the builtin devices and circuits, but also for reliability and deformability analysis. The results reveal an uneven bending-induced stress distribution at the top of the Si-chip that decreases from the central area towards the chipʼs edges along the bending direction, and increases towards the other edges. Near these edges, stress can reach very high values, facilitating the emergence of cracks causing ultimate chip failure.

High-performance giant magnetoresistive sensorics on flexible Si membranes

“…3(b)). Keeping in mind that the stress at the free surface of thin Si membranes is proportional to 1/r, 34 these findings indicate that the FWHM scales solely with the stress experienced by the sample coming from the deformation of the Si support.…”

“…3(b)) to Eq. (1), assuming M s ¼ 8.59 Â 10 5 A/m and a fracture point for Si at r % 325 MPa, 34 we obtain the value for the saturation magnetostriction constant to be k s ¼ 1.7 Â 10 À6 , which is an effective value for the GMR multilayer structure. This value is within the range of the figures previously reported for individual Ni-Fe thin films.…”

Towards bendable CMOS magnetic sensors

“…The uniaxial stress |σ 11 | distribution induced by bending is shown in the example presented in Figure 3. Although in the central region of the sensor the uniaxial stress is uniform, larger stress values can be noticed in the region close to the edges, located along the X 2 -axis, in accordance with [22].…”

“…P 12 =40×10 −11 Pa −1 for an N-well with n=4×10 16 cm −3 [16]. σ 11 and σ 22 are the in-plane stress σ components along [100] and [010] axes (see Figure 5). …”

CMOS Vertical Hall Magnetic Sensors on Flexible Substrate

“…With CMOS devices it is easier to meet the high performance requirements such as low-power and high-speed, which are needed in many wearable systems especially for wireless communication. Furthermore, it is possible to obtain conformable and wearable CMOS magnetic sensors system using ultra-thin technology which has been reported recently [11].…”